1. Field of the Invention
This invention relates generally to magnetic recording systems, like magnetic recording disk drives, and more particularly to an all-optical magnetic recording system that does not require an external magnetic field to switch the magnetization of the data bits.
2. Description of the Related Art
The more recent commercially available magnetic recording hard disk drives (HDDs) use perpendicular recording disks, wherein the magnetized regions are oriented perpendicular to the plane of the recording layer of the disk. The conventional perpendicular magnetic recording disk is a “continuous-media” (CM) disk wherein the recording layer is a continuous layer of magnetic material with perpendicular magnetic anisotropy that becomes formed into concentric data tracks containing the magnetically recorded data bits when the write head writes on the magnetic material. The read/write head is located on an air-bearing slider that is supported above the smooth disk surface on a thin film of air or “air-bearing” as the disk rotates.
Perpendicular magnetic recording disks with “bit-patterned media” (BPM) have been proposed to increase the data density. In BPM disks, the magnetic material on the disk is patterned into small isolated data islands such that there is a single magnetic domain in each island or “bit”. The single magnetic domains can be a single grain or consist of a few strongly coupled grains that switch magnetic states in concert as a single magnetic volume. This is in contrast to conventional CM disks wherein a single “bit” may have multiple magnetic grains separated by segregant material. For both CM and BPM disks, the magnetized regions or the individual data islands have their magnetizations switched by an external magnetic field from the disk drive's write head.
Recently, all-optical systems have been proposed that do not require an external magnetic field to switch the magnetization state of the media. The feasibility of all-optical systems has been demonstrated by several research groups using ferrimagnetic rare earth-transition metal (RE-TM) materials, for example GdFeCo alloys. It was shown that the reversal of the magnetization is achieved by applying a short laser pulse in the absence of an external magnetic field. However usage of these RE-TM materials in HDDs is not practical because they have limited magnetic anisotropy. Also, these materials are prone to corrosion due to their very strong affinity to oxygen. For example, the use of conventional HDD read heads requires at current areal densities a very close head-to-media spacing so that the thickness of the protective overcoat on the media must be less than 5 nm, which is not enough to prevent oxidation of RE-TM materials.
What is needed is an all-optical magnetic recording system with improved magnetic media.